The present invention relates to a distribution pressure controlling apparatus for controlling the distribution pressure in a distributing pipe network to obtain a constant distribution pressure.
Water from rivers is stored in a distributing reservoir through a water purification plant. Water thus stored is thereafter fed by a distributing pump and is supplied as service water to homes through distributing pipes embedded under roads near homes. Distributing pipes in a predetermined area are called a distributing pipe network, as a whole.
In order that service water can be used in homes, the pressure of service water should desirably be as constant as possible. Therefore, control must be performed so that the pressure or the distribution pressure in a distributing pipe network is constant. However, since the process gain in a distributing pipe network changes moment by moment in accordance with a demanded flow and the size of a change of the demand flow, it is difficult to control the distribution pressure to be constant.
An inference pressure control system and a PI pressure control system have been conventionally used as distribution pressure control systems as described above. In the inference pressure control system, a pressure loss Rf in a distributing pipe network is inferred and the distribution pressure P is obtained by a calculation of P=P.sub.0 -Rf.multidot.Q.sup.1.85 where the outlet pressure and the outlet flow of a distributing pump are respectively expressed as P.sub.0 and Q. Thereafter, the rotation speed of a distributing pump is controlled to adjust the outlet pressure P.sub.0.
Meanwhile, in the PI pressure control system, a calculation value is obtained by performing a proportional integral calculation based on a deviation between the distribution pressure P.sub.0 measured by pressure meters provided at predetermined positions in a distributing pipe network and a distribution pressure set value, and the calculation value is taken as an outlet target value P.sub.0. The rotation speed of a distributing pump is controlled such that the outlet pressure follows the outlet pressure target value P.sub.0.
However, in the former inference pressure control system, a relatively large difference appears between an inferred pressure loss and an actual pressure loss, and it is therefore difficult to obtain a desired distribution pressure.
In the latter PI pressure control system, even when the demanded flow and the change rate of the demand flow is large or small, control parameters of the proportional integral calculation, such as a proportional gain and an integral time are constant. Therefore, if the control parameters are once set in compliance with a situation such as nighttime in which the demanded flow or the change rate of the demanded flow is small, sufficient control response cannot be obtained in response to a situation such as daytime in which the demanded flow or the change rate of the demand is large.
Inversely, if the control parameters are once set in compliance with a situation such as daytime in which the demanded flow or the change rate of the demand is large, hunting may occur in a situation such as nighttime in which the demanded flow or the change rate of the demand is small.